This invention relates generally to controllers for electrically-driven compressors and more particularly to multipurpose compressor controllers for monitoring a variety of motor and compressor operating parameters and controlling the motor in accordance therewith.
One known compressor control apparatus is constructed for monitoring only the temperature of the compressor motor and de-energizing the motor in the event that an overtemperature condition is detected. Such overtemperature devices may take the form of overload relays which form a part of the motor starting contactor assembly and which are sensitive to motor current for selectively tripping the contactor in the event an excess current is detected which may result in undesirable motor heating. Another approach to the protection of compressor motors from excessive internal temperatures is to provide temperature sensors imbedded within the motor itself and a controller coupled thereto for receiving temperature related signals and de-energizing the motor if temperatures exceed prescribed limits.
Yet other compressor motor protective devices include separate equipments for protecting the motor against short cycle operation, for protecting the motor from overloads and/or protecting the compressor from accelerated wear in the event that the compressor lubricating oil system malfunctions. While these prior art devices have heretofore been satisfactory for compressor motor control they have failed to appreciate the advantages of providing an integrated compressor controller which is sensitive to a plurality of operating parameters and which is constructed and arranged to take advantage of the latest innovations in static switching devices. Additionally, the prior art has failed to appreciate the manner in which a controller may be constructed to incorporate certain self-diagnostic functions.
A compressor motor controller which combines a power supply together with hot motor, low voltage and low lubricating pressure detectors, which is capable of protecting the compressor motor against the undesirable effects of short cycle operation and which is capable of diagnostically detecting a fault in a motor temperature sensor would be a significant advance over the prior art.